ERP abnormalities of visual perception in Williams syndrome. Neuroreport. 2003;14:1773-7.
Disordered visual processing and oscillatory brain activity in autism and Williams Syndrome. Neuroreport. 2001;12(12):2697-700. Abstract
Disordered visual processing and oscillatory brain activity in autism and Williams Syndrome
Two developmental disorders, autism and Williams syndrome, are both commonly described as having difficulties in integrating perceptual features, i.e. binding spatially separate elements into a whole. It is already known that healthy adults and infants display electroencephalographic (EEG) gamma -band bursts (around 40 Hz) when the brain is required to achieve such binding. Here we explore gamma -band EEG in autism and Williams Syndrome and demonstrate differential abnormalities in the two phenotypes. We show that despite putative processing similarities at the cognitive level, binding in Williams syndrome and autism can be dissociated at the neurophysiological level by different abnormalities in underlying brain oscillatory activity. Our study is the first to identify that binding-related gamma EEG can be disordered in humans. NeuroReport 12:2697-2700 (C) 2001 Lippincott Williams & Wilkins.
Electrophysiological correlates of cross-linguistic speech perception in native English speakers. Behavioural Brain Research. 2000;111(1-2):13-23. Abstract
Electrophysiological correlates of cross-linguistic speech perception in native English speakers
The present study examined the electrophysiological responses that Native English speakers display during a passive oddball task when they are presented with different types of syllabic contrasts, namely a labial /ba/-dental /da/, a Hindi dental /da/-retroflex /da/ and a within-category (two /ba/ tokens) contrasts. The analyses of the event-related potentials obtained showed that subjects pre-attentively perceive the differences in all experimental conditions, despite not showing such detection behaviourally in the Hindi and within-category conditions. These results support the notion that there is no permanent loss of the initial perceptual abilities that humans have as infants, but that there is an important neural reorganisation which allows the system to overcome the differences detected and only be aware of contrasts that are relevant in the language which will become the subjects native tongue. We also report order asymmetries in the ERP responses and suggest that the percepts and not only the physical attributes of the stimuli have to be considered for the evaluation of the responses obtained. (C) 2000 Elsevier Science B.V. All rights reserved.
Electrophysiological correlates of category goodness. Behavioural Brain Research. 2000;112(1-2):1-11. Abstract
Electrophysiological correlates of category goodness
We report the results obtained from a behavioural and electrophysiological study. A synthesised continuum going from labial /ba/ to retroflex /da/ through dental /da/ was tested for category goodness. Native English speakers rated different tokens from each category as good, bad or ambiguous. The results showed that not all of the representatives of each category were ideal and that the categories tested have an internal structure. The electrophysiological study evaluated whether event related potentials (ERPs) mirrored the goodness judgements. During a passive oddball task, the same participants were exposed to native /ba/-/da/, Hindi dental /da/-retroflex /da/ and within-category /ba/-/ba/ contrasts. Results showed that participants pre-attentively perceive the differences in all cases, as shown by mis-match negativities (MMN), late positive deflections (LPD) or greater N1 and/or P2 components for deviant stimuli. Acoustic sensitivities, categorical perception and category goodness all contributed to the waveforms obtained. We attribute the ERP effects to a combination of (1) prototypes built from initial sensitivities, (2) reinforcement with exposure to one's native language and (3) no permanent loss of the initial boundaries explains the effects observed. (C) 2000 Elsevier Science B.V. All rights reserved.